Since this was a new project I wanted to keep it as simple as possible.
- Design a device that would travel ~25ft across the classroom on a 3/8" rope
- A fly wheel could be the only source of energy while the device was in motion on the rope
- The fly wheel could only be powered in a 1:1 ration by a Dewalt corded drill
- Chassis support
- What gear ratio to use
- Calculating the amount of kinetic energy of the flywheel
- Attaching to and riding the rope
The concept of friction over time and gear ratio was hard to explain to my students. Basically, i told them that the gear ratio doesn't change the amount of energy the flywheel has. That energy, in a perfect world, would move a mass a very specific distance. So the gear ratio is only really changing how long it takes to do that. Therein lies the problem though, time.
The more time (more rotations) the higher the total friction. Simply put, if the axle rotates 1 time you could measure 1x of friction. If it rotates 40 times the total friction would be 40x. Reducing the ratio reduces the friction and allows more energy to go into the movement of the walker.
Here is what i worked out.
My first test only went 18 in. By the equation Energy Kinetic=1/2IW^2, my flywheel produced 5.22J of energy. That meant the machine used .29 J/in. When I changed the gripper it travelled 52.5 in. Since I used the same fly wheel my new gripper reduced my energy per inch to .1 J/in. Using this number I started to figure out what I was going to need to make the distance.
While I was trying to go the distance, I also wanted to show some restraint and save material. So, I figured theory 2 was my going to be best. The new flywheel would produce 28J and would take my walker 290 inches. An interesting note about the flywheel; I used my CAD program (Onshape) to set the type of material (acrylic) and the penny calculator to predict the the mass of the flywheel before actually building it.
- Changing the gear ration effected the amount of friction
- Size of fly wheel
- Diameter of gripper
- Some numbers